Abstract
	The coking plant in U. S. Steel Košice, s.r.o., is the only cokery in Slovakia. It produces 50 till 65 m3/h of waste waters, mainly of organic origin, which are toxic to the biomass, but they are biologically decomposable. Coke waste water contains appreciable concentracions of pollutants such as phenols, cyanides, tiocyanate, hydrogen sulfide and ammonia.
	Raw waste water from cokery contains higher concentrations of toxic substances, than is the admissible value for the biological waste water treatment. This concentracion of pollutants is reduced to required attributes by preliminary treatment which includes the elimination of ammonia, sulphate and hydrogen cyanide.
	Trimming waste waters from coke production runs in a biological waste water purifier according to a project of Saarberg  Hõlter Wassertechnik GmbH Essen. 
	In the process of biological purifying phenols oxidate and decompose to carbonic acid and water. With the help of microorganism they produce certain amount of biological slime. Cyanides and sulphocyanides convert to ammonia, that biologically oxidates to nitrates and consequently reduces to gaseous nitrogen.    
	The contribution introduces the determination results, which state the optimal amount consumption of the chemical stock predetermined for pretreatment and biological purifying of waste water in a plant, as well as the comparison their projected and actual consumption, which brought the cost reduction at waste phenolammoniacal waters treatment to allowable pollution level.